The present invention relates generally to counterbalance systems for upwardly acting sectional doors. More particularly, the present invention relates to such a counterbalance system having cable storage drums which match the force of the counterbalance system with the gravitational force on the door during payout and retrieval of the cable interconnecting the door with the counterbalance system during movement of the door between a closed vertical position and an open horizontal position. More specifically, the present invention relates to operator-driven cable storage drums having differing diameter grooves about which a counterbalance cable is looped and attached to the door to one side of the drum and to an extension spring on the other side of the drum, whereby the linear force of the extension spring is matched to the nonlinear gravitational force exerted on a sectional door as it is moved between the closed vertical position and the open horizontal position.
Counterbalance systems for sectional doors have been employed for many years. Common examples of sectional doors are the type employed as garage doors in homes, commercial and utility building doors, and similar applications. Counterbalance systems originally solved the need for providing mechanical assistance in the instance of very large doors for commercial installations and garage doors for residential use, which were constructed of a relatively thick wood or metal components. More recently, counterbalance systems have been increasingly used to permit opening and closing operations by a single person and to facilitate the use of electric motors, preferably of limited size, to power the opening and closing of such doors.
Most such counterbalance systems utilize drums which carry cables attached to the garage door. Commonly, the drums are mounted above the frame defining the door opening with a drum positioned at each end of the door such that the cables may be conveniently connected proximate the lower lateral corners of the garage door. Basically, the door is moved toward the closed position blocking the door opening due to gravity acting on the door as it moves from a substantially horizontal open position above and inwardly of the door frame to a closed vertical position. The path of the door in opening and closing is commonly defined by a track arrangement which interacts with the rollers attached to the various sections of the door. The cable drums are classically interconnected with springs in a wide variety of ways so that they are progressively loaded as the door is lowered to prevent uncontrolled descent of the door and employ stored energy in the springs to assist in raising the door during the subsequent opening operation.
One type of counterbalance system which has been in use in the industry for many years employs extension springs. These extension springs are classically mounted adjacent the horizontal tracks or rails which support a door in the open position. The extension spring expands longitudinally as force is applied from a cable attached to a sheave at one end of the extension spring and proceeds to a single sheave positioned proximate the frame of the door which redirects the counterbalance cable to the bottom panel of the door. The force exerted by an extension spring upon elongation is essentially linear, whereas force exerted on a sectional door as it is moved upwardly and downwardly is a nonlinear gravitational force. With no possibility of adjustment during operation, the tension in conventional extension spring systems is optimal only at a small portion of its operating range with a compromise implemented between clearing the door out of the door opening when it is in the open position and maintaining it seated on the floor when the door is in the closed position. The result is that the available spring tension at neither the fully closed position nor the fully opened position can be optimized.
In the case of torsion springs operating on shafts mounted above the door in the closed position, the utilization of drums on such a shaft with a uniform diameter of the cable drum or grooves formed in the cable drum with a uniform diameter creates a condition where force applied by the torsion springs through the shaft and drums is essentially linear, whereas the gravitational force exerted on a moving sectional door is nonlinear. Therefore, as in the case of conventional extension spring systems, an undesirable compromise must be struck to effect satisfactory positioning of the door via spring tensioning in the fully opened and fully closed positions.
In an effort to obviate adjustment problems encountered in such conventional doors, spiral cable storage drums have been developed in recent years which have the first two or three outboard grooves on the cable drums designed with larger but decreasing minor diameters than the grooves extending inboard for the remainder of the drum surface. This allows the last coils of the counterbalance cable being removed from the drum during door closure to exert a greater force from the weight of the door against the tension on the counterbalance springs. In turn, this allows the counterbalance springs to be adjusted with extra tension to help displace the door from the door opening when the door is in the open position. However, the raised grooves engaged when the door approaches the closed position reduce the tension effects of the spring thereby allowing the door to seat and remain seated on the floor without uncontrolled lifting of the door.
Storage drums employing these grooves at one extent thereof require a maximum spring tension to achieve the multiple open and closed operating conditions discussed above. As a result, the normal operation of a sectional door through the majority of the operating range between positions proximate the opened and closed locations may result in the door being difficult to move or moving uncontrollably at certain locations. Thus, the adjustment of known sectional garage door counterbalance systems has remained a compromise of essentially conflicting considerations.
Therefore, an object of the present invention is to provide a counterbalance system employing extension springs which uses cable drums attached to a drive tube to replace the conventional front mounted pulleys for interconnecting the extension spring with the door. Another object of the present invention is to provide such a counterbalance system which adds control or regulation to door movement in allowing the energy from the two extension springs to be equally distributed to the door. A further object of the invention is to provide such a counterbalance system which allows the attachment of a jack shaft or header mounted operator to power the drive tube carrying the cable drums. Yet another object of the present invention is to provide such a counterbalance system wherein force distribution from the extension springs to the door through drums rotationally connected by the drive tube may prevent racking or canting of the door to a misaligned position in the event of the failure of the springs or cable of the counterbalance system.
Another object of the present invention is to provide a counterbalance system for sectional doors wherein the linear force of the springs is matched to the nonlinear gravitational force exerted on a sectional door as it is moved between the closed vertical position and the open horizontal position. A further object of the present invention is to provide such a counterbalance system wherein the pitch diameter of the grooves in the drums are varied over its length in a manner designed to optimize performance of the door during its final movement to the closed position, its final movement to the open position, and intermediate or transition positions therebetween. Still another object of the present invention is to provide such a counterbalance system having drum grooves configured to negate force from the remaining weight of the door against the counterbalance system as the door approaches the open position, to maximize the weight of the door as it approaches the closed position to assume and retain a seated closure, and to progressively balance the weight of the door against the counterbalance system.
Still another object of the present invention is to provide a counterbalance system for sectional doors wherein an operator-powered tube carrying cable drums has the cables interconnecting the springs with the door looped or reeved about the drums one or more times but not stored on the drums. A still further object of the present invention is to provide such a counterbalance system wherein the tension on the cables is adjusted such that the cable loop or loops on the drum do not slip in relationship to the drums during the full operating sequence of the door. Still another object of the present invention is to provide such a counterbalance system wherein spring tension operative on the door through the drum may be increased to prevent slippage of the cable loop or loops about the drum without affecting the counterbalancing of the door while concomitantly enhancing the ability of the increased spring tension to move the door out of the door opening in the fully open position of the door.
Still a further object of the present invention is to provide a counterbalance system having two mounted drums interposed between the counterbalance springs and the door, wherein the drums have grooves having differing minor diameters at different locations along the axial length of the drums. A further object of the present invention is to provide such a counterbalance system in which three separate arrays of grooves along the axial length of the drums provide optimized control of the door when moving between the closed vertical position and the open horizontal position. A still further object of the present invention is to provide such a counterbalance system which has improved operation at minimal additional cost, which is compatible with current industry safety standards, which can be designed for implementation with a variety of doors of differing sizes and weights, and which can be readily retrofit on existing doors having conventional extension spring counterbalance systems.
In general, the present invention contemplates an upwardly acting sectional door system having, a door having a plurality of hinged door sections movable between a closed vertical position and an open horizontal position, a drive tube mounted above the door in the closed vertical position, an operator selectively directionally rotatably driving the drive tube, cable drums mounted on the drive tube for rotation therewith by the operator, springs mounted in operative relation to the cable drums, and counterbalance cables reeved about the cable drums and interconnecting the springs and the door to counterbalance the door when moving between the closed vertical position and the open horizontal position.